Folding unit for tissue products

ABSTRACT

The present invention refers to a folding unit of a high-speed folding machine, for folding sheet-like products (S) made of tissue paper or the like. Such a unit comprises a first folding cylinder ( 3 ) with pneumatic means ( 5, 6, 5′, 6′ ) adapted to promote an orderly and precise release of the material in the folding step even at high speed.

TECHNICAL FIELD OF THE INVENTION

The present invention concerns the field of apparatuses for the production of paper products such as tissue paper, napkins or other products in general with high speed folding machines operating with a vacuum system.

BACKGROUND OF THE INVENTION

Such machines normally comprise two or more mutually cooperating folding cylinders, according to the type of product to be made. Work speed, and consequently productivity limitations, substantially depend upon the system for holding the material to be folded over the cylinders along the direction that is transverse with respect to the advancing direction. For such a purpose according to the prior art it is foreseen for there to be holes or slots along the periphery of the folding cylinders, which are connected to a vacuum source and are normally driven by sequential valves that are arranged at the axial end(s) of the cylinders themselves.

The most critical step is that in which the paper segments pass from a first cylinder, which normally provides also for a transversal cut of the paper, to a second cylinder so as to indeed execute the first transversal folding line. It is in this step that at the high speed at which such machines operate, there is the difficulty of ensuring a correct movement of the product from the condition in which it adheres to the first cylinder to that in which it adheres to the second cylinder. In order to minimise the risk of defects or malfunctioning it is necessary for the work speed to not exceed a set limit.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a system that solves such a problem, by providing a cross-wise folding unit for folding the product that makes it possible to increase production speed beyond the current production limits, obtaining at the same time a high quality product, i.e. without the defects caused today by the passage of the product through the folding cylinders.

According to the invention, such an object is achieved with the folding unit as defined in the first of the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and advantages of the folding unit according to the present invention shall become apparent from the following description of its embodiments, which are described as an example and not for limiting purposes, with reference to the attached drawings, in which:

FIG. 1 is a schematic side view of a folding unit according to the invention, with parts that have been removed for the sake of clarity;

FIG. 2 is a side view of a first folding cylinder;

FIG. 3 is a sectional view of the first cylinder according to the arrows Ill of FIG. 2;

FIGS. 4 and 5 are a side view and a sectional view according to the arrows V-V, respectively, of a first sequential valve, which is arranged on a first side (left side according to the view of FIG. 3) of the first folding cylinder;

FIGS. 6 and 7 are a side view and a sectional view according to the arrows VII-VII, respectively, of a second sequential valve that is arranged on a second side (right side according to the view of FIG. 3) of the first folding cylinder; and

FIGS. 8 and 9 are a side view and a sectional view according to the arrows IX-IX, respectively, of a single sequential valve that, according to an embodiment that is different from those of FIGS. 4 to 7, is arranged on one side of the first folding cylinder.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the above figures, a folding unit according to the present invention can advantageously provide for one or more adjacent channels which operate in parallel and it is fed with continuous bands of paper 1, having one or more layers (plies), with or without longitudinal folds with respect to the advancing direction.

The unit according to the present invention comprises, as known, a cutting cylinder 2 which cooperates with a first folding cylinder 3 so as to provide for cutting the product into segments with two blades 16 that are diametrically opposite one another (on the cutting cylinder 2) and two corresponding anvil grooves or counter-blades 17 (on the first folding cylinder 3), starting from a single band of paper 1. Subsequently, the same first folding cylinder 3 and a second folding cylinder 4 that counter-rotates with respect to the first cooperate in a tangential manner, at a pinch point in which the material is held by the second cylinder, so as to provide for folding the paper S obtained from the band 1 by means of cutting.

The first folding cylinder 3 comprises suction channels 5, 5′ which extend axially near to the work surface 3 a, for the passage of a vacuum that is suitable for keeping the band or segments of paper over such a surface. For such a purpose the channels 5, 5′ continuously cover the entire circumferential development of the cylinder, opening up on the surface 3 a through holes 6, 6′. The band of paper 1 is held in this way during cutting and thereafter the cut segment S is also held up to a release point from the first cylinder 3, with a vacuum of a sufficient strength, which is regulated through two sequential valves 7, 13 (not represented/visible in FIG. 1 but shown isolated in FIGS. 4 to 7) that are alongside one another and in contact on respective axial ends (or sides) of the aforementioned first cylinder.

Each valve is in practice a full fixed disc that blocks the ends of the channels 5 except for at suitably designated slots 9, 11, 14, which will be described in greater detail hereafter, which over certain set arcs of rotation make it possible for the vacuum flow to pass, said flow being generated and supplied by vacuum-generating devices that are arranged outside and are not represented. In any case, it should be noted that in FIGS. 5 and 7 intakes 8, 12, 15 for pneumatically connecting the slots to the vacuum-generating devices placed upstream.

The suction channels extensively involve the work surface 3 a, since they are spaced apart with a suitable density with respect to the evolution of the circumference. The majority of the channels, indicated with reference numeral 5, are open on the end side facing the first sequential valve 7 and are closed on the opposite side, so that the pneumatic circulation inside the aforementioned channels 5 is only determined by the first valve. Some channels, on the other hand, in particular two channels 5′ that are diametrically opposite one another in an immediately adjacent position with respect to the counter-blades 17 (upstream considering the rotation direction of the first cylinder) are open on the end side facing the second sequential valve 13 and are closed on the side of the first valve, so that the pneumatic circulation inside the (two) channels 5′ is determined only by the interference with the second valve 13.

The tangential cooperation point between the first and the second folding cylinder is that in which the segment S of paper is released from the first cylinder 3, through gripping of the second cylinder 4 along a transversal intermediate line; consequently the paper becomes folded along such a line on the second cylinder 4. For such a purpose it is foreseen for there to be, in a suitable position on respective portions of the second folding cylinder 4, sets of axial channels 20 and holes 21 which open radially on the work surface 4 a of the cylinder, which are capable of providing for gripping or pinching the sheet through suction.

Returning now to the two sequential valves 7, 13 and to the relative slots, the first sequential valve 7 has two consecutive slots 9, 11, which are separated by an interruption, i.e. by a solid separating wall 10, that overall extend for an arc of rotation of around 270°. A first slot 9 occupies around 180° of rotation and, in it, through the intake 8, a high vacuum is generated, which results through the channels 5 and the holes 6 in a suction by the work surface 3 a on the paper S.

The subsequent slot 11 that extends for an arc of rotation of around 90° (following the passing on the pinch point by the second cylinder 4) is, on the other hand, fed through the intake 12 with a rough vacuum or no vacuum (according to the characteristics of the material being processed), so as to transmit, again through the channels 5 and the holes 6, low or null suction that promotes the release of the paper.

Instead, as far as the second sequential valve 13 is concerned, only one slot 14 is provided, for the generation of high vacuum that is transmitted through the two channels 5′ and relative holes 6′. This slot 14 extends by covering the same 180° of the first slot 9 of the first valve, and further on develops over a substantial part of the 90° of the second slot 11. With respect to the latter, the slot 14 ends with an advance of a certain angle (typically between 15° and 30°, thus corresponding to a rotation angle downstream of the release point comprised between 60° and 75°).

In such a way, through the holes 6′ that are immediately adjacent to the cut performed at the counter-blade 17, and thus in the immediate proximity of the head or frontal edge of the segment S (i.e. the edge that advances at the front when using the rotational advance direction as a reference), a suction is exerted which firmly holds such edge over the first cylinder (see indeed the operation step depicted by FIG. 1) for the entire displacement, also downstream of the folding point and also and especially in the step of incipient folding, when on the remaining part of the segment there is progressively less suction so as to promote the release (effect of the second groove 11 of the first aforementioned valve 7).

The operational behaviour of the unit according to the invention is then immediately clear to a man skilled in the art, considering that anything that was not been specifically described is indeed analogous to what is well known in the conventional units. Thanks to the feature introduced by the second sequential valve, in a structurally very simple manner, there is the possibility of avoiding deformations of the front edge even at high production speed, with consequently lower wastes and an increase in the quality of the product.

According to FIGS. 8 and 9, in a possible different embodiment the functions of the second sequential valve can be integrated on a single valve 107 thorough a double array of slots, which are radially offset to a greater or lesser extent. In such figures the slots 109 and 111, with the relative suction intakes, correspond to the previous slots 9 and 11 of the first embodiment, whereas a double slot 114 a, 114 b operationally corresponds to the slot 14 of the first example. Two consecutive and separated segments 114 a, 114 b are used in this case for a possible differentiation of suction (higher or lower vacuum) in two respective advancing steps upstream and downstream of the release/pinch point, respectively, also in connection with the hold at the front edge. Such a differentiation, which can be useful according to the type of material being treated, can also be obtained in the first embodiment by separating the groove 14 into two distinct segments.

Obviously, the structure of the first folding cylinder (not shown) must be correspondingly adapted, since in this case the two channels corresponding to the channels 5′ of the first embodiment, i.e. the channels that are suitable for holding the front edge of the segment and for communicating with the slots 114 a, 114 b, are made in a position that is radially more centred with respect to the other normal peripheral channels which correspond to the channels 5 of the first embodiment and in which there is the pneumatic opening/closing action of the slots 109 and 111.

It is worth underlining that by high vacuum, in the present description, it is meant a high vacuum, ultra high vacuum or extremely high vacuum according to the definitions that are commonly and conventionally used in the field.

The present invention has been described with reference to preferred embodiments thereof. It should be understood that there can be other embodiments that belong to the same inventive core, within the scope of protection defined by the appended claims. 

1. A folding unit for folding sheet-like products (S) made of tissue paper or the like, comprising a first folding cylinder and a second folding cylinder mutually counter-rotating and tangentially cooperating in a release and pinch point to carry out the folding of said products (S), said first folding cylinder comprising a work surface, paper material cutting means extending along respective generatrices of the cylinder regularly spaced around the circumference, and vacuum means adapted to hold said products over said work surface, wherein said vacuum means comprise first vacuum means extensively distributed over said work surface adapted to transmit a high vacuum over a determined rotation angle of the first cylinder upstream of said release point, and to transmit a rough vacuum or no vacuum over a determined rotation angle downstream of said release point, and second vacuum means, pneumatically independent with respect to said first vacuum means, arranged immediately downstream of respective cutting means and adapted to transmit a high vacuum at least over a determined rotation angle downstream of said release point.
 2. The unit according to claim 1, wherein said determined rotation angle in which said second vacuum means transmit a high vacuum downstream of said release point is between 60° and 90°.
 3. The unit according to claim 2, wherein said rotation angle is between 60° and 75°.
 4. The unit according to claim 1, wherein the second vacuum means are also adapted to transmit a rough or medium vacuum over a determined rotation angle upstream of said release point.
 5. The unit according to claim 1, wherein said first and second vacuum means comprise axial channels that open at said work surface through radial holes, the pneumatic communication between said axial channels and external vacuum generation means being blocked by at least one selective operation valve comprising a slotted fixed disc arranged over at least one axial end face of the first folding cylinder.
 6. The unit according to claim 5, wherein said axial channels of said first and second vacuum means open at mutually opposed axial ends of the first folding cylinder, and are selectively shut by respective operation disc valves arranged at respective and opposed axial end faces of the cylinder.
 7. The unit according to claim 5, wherein said axial channels of said first and second vacuum means open at a same axial end of the first folding cylinder, in positions having mutually different distances from the center, and are selectively shut by a single operation disc valve with two ranks of arc-shaped slots having different radius.
 8. A method for folding sheet-like products made of tissue paper or the like by means of a first folding cylinder and a second folding cylinder mutually counter-rotating and tangentially cooperating in a release and pinch point to carry out the folding of said products (S), the method comprising: cutting the paper material in segments (S) on said first folding cylinder, said segments having a head edge which is arranged frontally with respect to the rotational advance direction; exerting a vacuum over a work surface of the first folding cylinder to hold said segments (S) over said work surface; and pinching said products by said second folding cylinder when a release portion of said work surface passes in said release and pinch point, wherein a high vacuum is extensively generated over said work surface for a determined rotation angle of the first cylinder upstream of said release point and a rough or no vacuum is extensively generated over said work surface for a determined rotation angle of the first cylinder downstream of said release point, and wherein said front edge of a segment (S) is also held locally by generating a high vacuum at least for a determined angle of rotation downstream of said release point, independently from the extensive generation of the rough or no vacuum in the same angle of rotation.
 9. The method according to claim 8, wherein said determined rotation angle in which said front edge is locally held downstream of said release point is between 60° and 90°.
 10. The method according to claim 9, wherein said rotation angle is between 60° and 75°. 